The word "km" is an abbreviation for "kilometer," which is a unit of measurement used to determine distance. It represents a measurement that is commonly used to represent longer distances, such as between cities or countries. Full definition
This huge jet stream also extends about 70,000 km from north to south, more than five times the size of our planet. (sciencedaily.com)
As for power lines, for each wind farm you need to build tens of km of new ones, increasing the death toll from these structures as well. (savetheeaglesinternational.org)
Keep in mind though that lightning has been known to strike 5 or more km away from a storm. (armourinsurance.ca)